This patent document relates to optical gyroscopes for optically sensing rotation.
Sensing of rotation can be used in a wide range of applications, including, e.g., navigation, motion sensing, motion control including object stability control, game console controllers, hand-held devices such as smartphones. Optical gyroscopes can be designed to use rotation-induced changes in the optical interference pattern of two counter-propagating optical beams to measure the rotation. Many optical gyroscopes are based on an optical Sagnac interferometer configuration including various interferometric fiber-optic gyroscopes (IFOGs). Such optical gyroscopes can be designed without moving parts and thus eliminate the wear and tear in other gyroscopes with an oscillating proof mass or a moving component. IFOGs are commercialized and in mass production and can be used in various military and civilian applications, including applications for aircrafts, vessels, and land vehicles for precision rotation rate and angle detection.
FIG. 1 shows an example of an optical gyroscope based on a Sagnac interferometer formed by an optical ring loop in free space with reflectors and in an optical fiber loop, respectively. The Sagnac interferometer in FIG. 1 uses an input beam splitter (BS1) to receive input light for the Sagnac interferometer and to direct the returned light from the Sagnac interferometer into the photodetector (PD) for detecting the interference signal caused by the Sagnac interferometer. A second beam splitter (BS2) is coupled to the optical ring loop of the Sagnac interferometer as shown to produce two counter propagating beams. An optical polarizer is placed between the two BS devices BS1 and BS2 to insure the polarization of the light at the second BS (BS2) to provide an equal splitting of the optical power between the two optical beams coupled into the optical ring loop. The second BS2 splits the polarized input light into two counter propagating beams having light in the same polarization in the optical ring loop and the two counter propagating beams are recombined at the same BS (BS2) to optically interfere with each other due to the presence of light in the same polarization in the two beams. A portion of this recombined light at the BSs with the optical interference information is directed into the first BS (BS1) which directs at least a portion of the recombined light into the PD for detection. To increase the sensitivity and reliability, the optical ring loop can be designed to have a long ring loop length. For example, a relatively long length of fiber coil (e.g., hundreds to thousands meters of fiber) may be used to form the optical ring loop.